The invention relates to routing of covert flight paths for maximum terrain masking. More particularly, the invention relates to use of digital terrain elevation data to generate a costing surface which allows superior routing of covert flight paths.
Digital terrain elevation data (DTED) is a digital representation of the topography of a geographical region. DTED is produced from satellite photographs or other means and is available through the Defense Mapping Agency to government contractors on a need-to-know basis. DTED comprises a plurality of digital data points laid out in a grid with a spacing typically on the order of 800 meters between points.
When routing flight paths for covert operations, it is desirable to route the paths such that maximum terrain masking is achieved. Particularly, it is desirable to avoid highly visible areas such as ridge tops and wide open areas.
According to the prior art, it is known to route covert flight paths using DTED such that the flight path is always in the lowest local area. This routing method rests on the assumption that the best terrain masking will always be at the lowest local elevation. However, this assumption is not always true, and thus the prior art method frequently results in less than optimum routing of flight paths. For example, consider an airplane flying perpendicular to the plane of the paper along a line through point A in FIG. 1. Because of the high valley created by parallel ridges R1 and R2, the flight path through point A will have excellent terrain masking. Under the prior art assumption that the lowest local elevation has the best terrain masking, however, the prior art routing method will cause the airplane to move from position A to the lower position B in the adjacent valley. Clearly, despite the fact that position B is lower than position A, the terrain masking in the open valley is significantly inferior to the terrain masking at position A. Moreover, in order to move from position A to position B, the flight path must move over ridge R1, i.e., through a highly visible area where detection is likely. Thus, the prior art routing method cannot be used to provide reliable terrain-masked covert flight paths.
The use of local minimums in DTED to route covert flight paths also neglects the importance of the roughness or "flyability" of the terrain. Where the surface of the local minimum is very rough, it will be difficult for the aircraft to maintain a low altitude flight path. Flying at an increased altitude over low but rough terrain may in many cases be more visible than flying at a lower altitude over flatter, higher terrain. Known methods of routing covert flight paths do not satisfactorily address this issue.